The field of the invention relates generally to annular vessels, and more specifically, to a method and systems for sealing annular spaces inside a radiant syngas cooler.
In quench gasifiers, syngas is passed through a water bath where it is cooled down to a temperature which can be handled by the downstream systems. The quench water also retains some of the solids carried by syngas and assists in solidification of the slag which is transferred to the slag crusher. After passing through the quench water syngas flows from the Radiant Syngas Cooler (RSC) through a syngas transfer line. An annulus exists between the heat transfer surfaces (tube cage) which confine the hot gas path and the outer shell (vessel) of the RSC. This annular space is continuously purged with nitrogen to prevent syngas accumulation in this area, which could result in significant corrosion.
During unsteady events, syngas can migrate into the annulus between the tube cage and the vessel. Such a condition could result in damage to the tube cage due to dew point corrosion (H2S and HCl which can exist in syngas are very corrosive and tend to condensate at a temperature of approximately 450° Fahrenheit to approximately 600° Fahrenheit (230-320° Celsius). During severe upsets of the flow through the RSC, for example, during light off, syngas and water could reach the annular space. Water greatly increases the risk of corrosion of the annular space. To mitigate these risks and eliminate other hazards, the RSC annulus is continuously purged with a purge fluid such as nitrogen. Nitrogen is discharged at the top of the annulus, flows through the annular space between the tube cage and the vessel and mixes with syngas to dilute the corrosive components of the syngas. The purge fluid then mixes with the syngas as it flows through the syngas transfer line. Purge flow is initiated before light off to assure that oxygen (air) is removed before syngas production starts. Many versions of seals have failed to provide adequate protection to the annular space and adequate thermal expansion margin.